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Method:
Type AZ . The following screen display appears while the program steps the azimuth drive towards
its internal optically-sensed reference flange:
*** zeroing azimuth
press Del to abort
The operator can abort the operation by pressing the DEL (delete) key; the program will return to
the previously displayed menu. When the program has located the reference flange it compares
the predicted and actual flange positions, then displays the step discrepancy on the screen for
about 5 seconds:
*** discrepancy = n
AZIMUTH ZEROED AT HH:MM:SS DISCREPANCY = N
N will usually be a small integer lying in the range -10 < n < 10. (The Tracker stepper-motor gearing
is approximately 15000 steps per revolution, so a discrepancy of 10 steps corresponds to a
positional error of 0.2°). N will be much larger if the Brewer has recently been reset or if the Tracker
has been physically perturbed (eg power interruption).
The Azimuth Tracker then returns to the solar azimuth and the previously active menu is displayed.
SR: AZIMUTH TRACKER STEPS-PER-REVOLUTION CALIBRATION
The SR test determines the number of steps required for the azimuth drive motor to turn the
Brewer through 360° in azimuth. This test establishes the steps-per-revolution constant which is
used by the Brewer program to orient the Brewer in azimuth to within ±1 minute of arc.
An opto-sensor located inside the Azimuth Tracker detects a reference flange on the stationary
drive-wheel. The azimuth drive motor is 'zeroed' on this reference, then stepped forward until the
flange is again detected on the next revolution. At this point the tracker has rotated exactly 360°,
and the steps-per-revolution constant has been determined.
The SR routine can only be accessed if the instrument configuration (IC command) has been setup
to include an Azimuth Tracker.
Method:
Type SR to initiate the steps-per-revolution test. The first portion of the calibration proceeds exactly
as for AZ . Once the internal optically-sensed reference flange has been detected, the azimuth
step-count is set to zero and the drive motor is stepped forward until the flange is again detected
after 360° of rotation. During the forward search the following screen message is displayed:
*** finding az steps/rev
press del to abort
It takes approximately 30 seconds to rotate through 360°. (The operator may abort the steps-per-
revolution calibration at any time by pressing the DEL key.) Calibration results are displayed as
follows:
steps/rev measured at 14675
old value = 14678
do you want new value saved? - y/n
MKIII OPERATOR'S MANUAL
APPENDIX F FACTORY TESTS
107
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